Copper conductor paste and production method of copper conductor film

ABSTRACT

A conductor paste comprising a high-polymer composite obtained by dispersing super-fine-granulated copper oxide in a polymer without being aggregated, mixed copper powders mainly composed of a base copper powder having a mean particle size of 1 to 10 μm added with at least one kind of an auxiliary copper powder having a mean particle size smaller than that of the base copper powder, and an organic solvent, wherein the wight ratio of the mixed copper powders to copper oxide in the high-polymer composite is 5 to 50 to 1 of copper oxide and the total amount of copper oxide and the mixed copper powders is 50 to 90% by weight of the conductor paste, and a production method a conductor film by coating the conductor paste on the surface of a substrate and after pre-burning the conductor paste under temperature raising, burning the conductor paste to form the conductor film on the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a copper conductor paste and aproduction method of a copper conductor film, and more specifically to acopper conductor paste forming conductive paths of a copper film byprinting the copper paste onto a ceramic substrate followed by burningand also to a production method of a copper conductor film.

2. Description of the Related Art

Recently, as a conductive paste being applied to electric and electronicparts such as ceramic substrate hybrid IC, ceramic condensers, etc., anAg--Pd paste mainly composed of silver and palladium, a gold paste, anAg--Pt paste mainly composed of silver had platinum, and a copper pasteare used.

In these pastes, the Ag--Pd paste is a typical paste as a wiring use buthas some disadvantages. For example, when the paste is used as wiring ona substrate, silver is ionized with moisture in air. Consequently, aphenomenon called a migration is caused in which the ionized silvermigrates to the adjacent conductor paths to cause short-circuiting.Thus, the distance between the conductor paths cannot be narrowed. Also,in a soldering portion for loading or connecting other part onto aconductor path, silver is liable to be corroded with a soft solder andthe Ag--Pd paste is inferior in the soldering resistance.

Also, in the case of adhering the foregoing Ag--Pd paste to a substrate,since fine metal particles of a micron size cannot essentially beadhered to a ceramic substrate by causing a reaction, about 4 to 10% byweight a glass frit is compounded with the paste and the glass fritexisting on the substrate after printing fives a function of adheringthe substrate and the metal film after burning. However, on the otherhand, since a large amount of the glass frit remains in the metal filmafter burning, there occur the problems that the electric resistance ofthe metal film is increased. Also, since the metal film is adhered tothe substrate with a glass layer, a strain is liable to occur by thedifference in the thermal expansion and the thermal shock resistance isweakened.

As a paste partially solving such disadvantages, a copper paste isknown. The paste is composed of a composition formed by dispersingcopper, a glass frit, and a non-copper material such as tungsten,molybdenum, rhenium, etc., in an organic solvent as described, e.g., inUnexamined Japanese Patent Publication (kokai) No. Sho. 60-70746. Alsothe paste is composed of a composition formed by dispersing metalliccopper particles coated with copper oxide, copper oxide particles, and aglass powder in an organic solvent as described in Examined JapanesePatent Publication (kokoku) No. Hei. 3-50365.

However, since in the foregoing copper paste, a large amount of,preferably from 5 to 10% by weight, the glass frit is added as a glasspowder and functions for adhering the substrate and the metal film, whenthe copper paste is coated on a substrate and a metal film is adhered tothe substrate by burning, a large amount of the glass frit remains inthe metal film after burning and thus there still remain problems thatthe electric resistance of the metal film is high, also the glass layerexisting at the interface between the metal film and the substratecauses a strain by the difference in the thermal expansion, and the heatresistance and the thermal shock resistance are weakened. The thermalshock resistance is evaluated by the adhesive force between the metalfilm and the substrate after transferring the substrate having adheredthereto the metal film from a low-temperature atmosphere to ahigh-temperature atmosphere and repeatedly transferring the substrate tothe opposite direction.

Also, since a lead borosilicate glass having a low softening point isused as the foregoing glass frit, in the soldering step for an oxidationprevention and Au wire bonding, lead in the foregoing glass inhibitssoldering.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a conductive paste whichnot only improves the adhesive force between a metal film and asubstrate but also lowers the electric resistance of the metal film, isexcellent in the thermal shock resistance, and does not cause anytroubles in processing after soldering, etc., and also to provide aproduction method of a copper conductor film.

A copper conductor paste of the present invention is comprised of: apolymer composite including a polymer and super-fine-granulated copperoxide, the super-fine-granulated copper oxide being dispersed in thepolymer; mixed copper powder including base copper powder having a meanparticle size in a range of 1 to 10 μm and at least one kind ofauxiliary copper powder having a mean particle size range smaller thanthat of the base copper powder; and an organic solvent; wherein a weightratio of the mixed copper powder to copper oxide in the polymercomposite is in a range of 5 to 50 to 1 of copper oxide, and a totaladdition amount of copper oxide and the mixed copper powder is in arange of 50 to 90% by weight of the conductor paste.

In the conductor paste of the present invention, the super-fineparticles of copper oxide having particle sizes do not cause separationand precipitation in the paste by the interaction with the polymer andalso the conductor paste adheres to a ceramic substrate by causing areaction owing to the high reactivity of the super-fine particles to beable to form a conductor film having a large adhesive force. Also, byadding mixed copper powders each having a different mean particle sizerange, the auxiliary copper powders fill the voids and spaces formed bythe arrangement of the base copper powders, whereby a conductor filmhaving no inside defects and having a good burned tightness can beobtained.

DETAILED DESCRIPTION OF THE INVENTION

Detailed description of the present invention will be described asfollows.

A copper conductor paste of the present invention includes a highpolymer composite obtained by dispersing super-fine-granulated copperoxide in a polymer without being aggregated, mixed copper powders mainlycomposed of a base copper powder having a mean particle size range offrom 1 to 10 μm added with at least one kind of an auxiliary copperpowder having a mean particle size range smaller than that of the basecopper powder, and an organic solvent. In the copper conductor paste,the weight ratio of the mixed copper powder to copper oxide in theforegoing high polymer composite is from 5 to 50 to 1 of copper oxide,and also the total addition amount of copper oxide and the mixed copperpowder is from 50 to 90% by weight in the conductor paste.

In addition, in the present invention, a glass powder is added to theconductor paste as described above, and the addition amount of the glasspowder is from 0.1 to 1.0 part by weight to 100 parts by weight of thetotal addition amount of copper oxide and the mixed copper powder.

Further, a production method of a copper conductor film of the presentinvention uses a conductor paste which is produced by dispersing in anorganic solvent at least a high polymer composite obtained by dispersingsuper-fine-granulated copper oxide in a polymer without being aggregatedand mixed copper powders mainly composed of a base copper powder havingan average mean particle size range of from 1 to 10 μm added with anauxiliary copper powder having a mean particle size range different fromthat of the base copper powder. The surface of a substrate is coatedwith the conductor paste thus produced. After pre-burning the conductorpaste under temperature raising, the conductor paste is burned to form aconductor film on the surface of the substrate.

Also, the high polymer composite being used in the present invention maybe a high polymer composite produced by preparing a thermodynamicallynon-equilibrated high polymer layer, and after adhering a metal layer ofcopper onto the surface of the polymer layer, heating the polymer layerto stabilize the high polymer layer, whereby super-fine particles ofcopper oxide obtained by super-fine granulating from the metal layer aredispersed from the metal layer in the polymer without being aggregated.

Furthermore, it is preferable that mixed copper powders includes from 80to 98% by weight a base copper powder having a mean particle size in arange of from 2 to 10 μm based on the amount of the mixed copperpowders, from 1 to 10% by weight an auxiliary copper powder having amean particle size range of from 0.7 to 2 μm based on the amount of themixed copper powders, and from 1 to 10% by weight an auxiliary copperpowder having a mean particle size range of from 0.5 to 1 μm based onthe amount of the mixed copper powders.

The high polymer composite which becomes the first component of theconductor paste of this invention is a composite produced by preparing athermodynamically non-equilibrated high polymer layer and after closelyadhering at least a copper metal to the surface of the high polymerlayer, heating the high polymer layer to stabilize the high polymerlayer, whereby copper oxide composed of Cu₂ O or CuO having particlesizes of not larger than 100 nm, and preferably from 1 to 50 nm formedby super-fine-granulated from the copper metal is dispersed in thepolymer without being aggregated. The content of super-fine-granulatedcopper oxide is not more than 90% by weight, and preferably from 0.01 to90% by weight. Super-fine-granulated copper oxide has a high reactivityat a low temperature, thereby the copper oxide accelerates sintering ofthe copper powder, and also adheres to a substrate by causing a reactionto form an extremely adherent conductor film.

In the case of producing the high polymer composite described above, itis necessary to form the high polymer layer in a thermodynamicallynon-equilibrated state. Practically, there are a vapor deposition methodof melting and evaporating a high polymer by heating it in a vacuum andsolidifying the high polymer layer on a substrate, a melting, quenchingand solidifying method of melting a polymer at a temperature higher thanthe melting point of the polymer, quenching the polymer by immediatelyplacing the molten polymer in that state in liquid nitrogen, etc., andattaching the polymer layer onto a substrate, etc.

In these methods, in the case of the vacuum vapor deposition method, thepolymer layer can be obtained on a substrate such as a glass plate,etc., using an ordinary vacuum vapor deposition apparatus at a vacuum offrom 10⁻⁴ to 10⁻⁶ Torr and a an evaporation speed of from 0.1 to 100μm/minute, preferably from 0.5 to 5 μm/minute. In the melting,quenching, and solidifying method, a polymer is melted and the polymerlayer is obtained by cooling the molten polymer at a speed higher thanthe critical cooling speed specific to the polymer. The polymer layerthus obtained is placed in a thermodynamically unstable non-equilibratedstate and transfers to the equilibrium state with the passage of time.

The high polymer (or polymer) being used in this invention is, forexample, nylon 6, nylon 66, nylon 11, nylon 12, nylon 69, polyethyleneterephthalate (PET), polyvinyl alcohol, polyphenylene sulfide (PPS),polystyrene (PS), polycarbonate, and polymethyl methacrylate, and thepolymer having the molecular cohesive energy if at least 2,000 cal/molis preferred. The polymers include ordinary crystalline polymers andnoncrystalline polymers. In addition, the molecular cohesive energy isdefined in detail in Kagaku Binran Oyo Hen (Chemical Handbook,Application Chapter), page 890, edited by Chemical Society of Japan(published 1973).

Then, the foregoing thermodynamically non-equilibrated high-molecularlayer is transferred to the step of adhering a metal layer of copper tothe surface thereof. In the step, a metal layer of copper is laminatedon the high polymer layer by a method of vapor-depositing a metal layerof copper onto the high polymer layer by a vacuum vapor depositionapparatus or a method of directly adhering a metal foil or a metal plateof copper onto the high polymer layer.

The composite of the high polymer layer and the metal layer of copperadhered onto the high polymer layer is heated to a temperature of fromthe glass transition point of the high polymer to the pour temperatureto stabilize the high polymer layer. As the result thereof, the metallayer of copper becomes super-fine particles of copper oxide havingparticle sizes of not larger than 100 nm and the maximum particle sizedistribution in the region of from 1 to 50 nm, and the super-fineparticles of copper oxide diffuse and permeate into the inside of thehigh polymer layer. This state continues until the high polymer layercompletely stabilized, and the metal layer of copper adhered to the highmolecular layer reduced the thickness and is vanished finally. Theforegoing super-fine particles are distributed in the inside of the highpolymer layer without being aggregated. In this case, the content of thesuper-fine particles is from 0.01 to 80% by weight but the contentthereof can be controlled by changing the preparation condition of thehigh polymer layer or changing the thickness of the metal layer ofcopper.

In addition, when the high polymer layer is heated in the step, thehigh-molecular layer shows a specific color by the interaction with thesuper-fine particles of copper oxide, which shows that the super-fineparticles of copper oxide is permeated in the inside of the high polymerlayer. Also, the color can be changed by the particle sizes of thesuper-fine particles of copper oxide and the kind of the polymer.

In the present invention, as the production method of the high polymercomposite, there are not only the methods described above but also amethod of preparing super-fine particles of a noble metal by avapor-phase method belonging to a melt vaporization method, aliquid-phase method belonging to a precipitation method, a solid-phasemethod, or a dispersion method and mechanically mixing the super-fineparticles with a solution or a molten liquid of a high polymer, a methodof simultaneously evaporating a high polymer and a noble metal andmixing them in the vapor phases, etc.

Also, the mixed copper powders which are the second component of theconductor paste of the present invention are mixed copper powdercomposed of a copper powder having a mean particle size range of from 1to 10 μm as the base added with at least from 1 to 3 kinds of auxiliarycopper powders each having a mean particle size range smaller than thatof the base copper powder. The specific mixed copper powders arecomposed of a base copper powder having a mean particle size range offrom 2 to 10 μm and having the largest mean particle size, a firstauxiliary copper powder having a mean particle size range of from 1 to 2μm and having the next larger mean particle size, and a second auxiliarycopper powder having a mean particle size range of from 0.5 to 1 μmwhich is the smallest mean particle size.

In the mixed copper powders, the content of the base copper powder isfrom 80 to 98% by weight, the content of the first auxiliary copperpowder is from 1 to 10% by weight, and the content of the secondauxiliary copper powder is from 1 to 10% by weight. In particular, theauxiliary copper powder being used in this invention is not limited tothe auxiliary copper powders described above but, for example, a thirdauxiliary copper powder having a mean particle size range of not largerthan 1 μm may be also used. The form of each copper powder of the mixedcopper powders described above is preferably near a relatively sphericalform. This is for arranging the copper powders with less voids. The useof the mixed copper powders each having a different mean particle sizerange has an advantage that since the auxiliary copper powders having asmaller mean particle size range fill the voids and spaces formed by thearrangement of the base copper powders having the largest mean particlesize range, the conductor film after burning has no inside defects andburned tightness becomes good.

If the mean particle size range of the base copper powder is over 10 μm,the mixed copper powders are reluctant to be influenced by oxidation andthe width for establishing the condition of pre-burning may bebroadened. However, the mixed copper powders are not sufficientlysintered at a low temperature and the burned tightness becomesinsufficient to lower the adhesive force of the conductor film and thesubstrate. Also, in this case, the copper powders are crushed by an inkrolling step to thereby form copper foils, which sometimes cause meshclogging at screen printing. On the other hand, if the mean particlesize range of the base copper powder is less than 1 μm, the totalparticle area of the mixed copper powders become too large, whereby theinfluence of oxidation is increased and the electric resistance becomeshigh.

Also, if the addition amount of the base copper powder is over 98% byweight, the mixed copper powders are not sufficiently sintered at a lowtemperature to cause the insufficiency in the burned tightness to lowerthe adhesive force between the conductor film and the substrate. On theother hand, if the addition amount of the base copper powder is lessthan 80% by weight, the total particle area of the mixed copper powdersbecomes too large and the same troubles as described above occur. Inaddition, the auxiliary copper powders are added for filling the voidsand spaces formed in the case of arranging the base copper powders andthe mean particle sizes. Accordingly, the addition amount of theauxiliary copper powders give a large influence on the function.

Also, in the present invention, for further improving the adhesive forcebetween the conductor film and the substrate, a glass powder such as aglass frit may be added to the mixed copper powders. The glass powder,which is a third component, has a mean particle size of from 1 to 10 μmand a softening point of from 500° to 700° C. and may contain lead butconsidering soldering in the post step, it is preferred that the glasspowder does not contain lead, which hinders soldering.

The addition amount of the foregoing glass powder is from 0.1 to 5.0part by weight to 100 parts of the total addition amount of copper oxideand the mixed copper powders. If the addition amount is over 1.0 part byweight, the adhesive force between the conductor film and the substrateis improved. However, since the glass powder yet remains in the insideof the conductor film after burning, the electric resistance of theconductor film tends to increase, also the glass layer existing at theinterface between the conductor film and the substrate is liable tocause strain by the thermal expansion difference, and the thermal shockresistance is weakened. On the other hand, if the addition amount of theglass powder is less than 0.1 part by weight, the improvement of theadhesive force cannot be obtained.

The organic solvent being used in the present invention is ahigh-boiling solvent such as metacresol, dimethylimidazolidinone,dimethylformamide, carbitol, terpinol, diacetone alcohol, triethyleneglycol, paraxylene, etc.

The conductor paste of the present invention can be obtained bydissolving the high polymer composite in the foregoing organic solventand, after uniformly dispersing the super-fine particles of copper oxidein the solution, the mixed copper powders or the mixed copper powdersand a glass powder are added to the dispersion with stirring followeduniformly mixing by an ink roll. Copper oxide having the particle sizedoes not cause the separation from the polymer and the precipitation inthe conductor paste by the interaction with the polymer.

In this case, the addition amount of the mixed copper powers isdetermined based on the amount of copper oxide in the high polymercomposite and the weight ratio of the mixed copper powders to copperoxide is from 5 to 50 to 1 of copper oxide. If the weight ratio is lessthan 5, the contents of the organic components in the conductor pasteare increased and the electric resistance is increased. On the otherhand, if the weight ratio is over 50, the content of copper oxidecontributing to adhesion is reduced and thus the burned tightness of thecopper powders is reduced.

Also, the total addition amounts of copper oxide and the mixed copperpowders is from 50 to 90% by weight of the conductor paste. If theaddition amount is less than 50% by weight, the contents of the organiccomponents become large and the burned film becomes porous. On the otherhand, if the addition amount is over 90% by weight, the printability isreduced.

The conductor paste obtained is coated on a ceramic substrate such asalumina, aluminum nitrate, silicon carbonate, silicon nitride, saialone,barium titanate, PBZT, etc., by screen printing, etc. In the procedureof screen printing, a printing substrate is placed under a screen (e.g.,polyester plain weave fabric, 255 mesh) horizontally disposed. Afterplacing the conductor paste on the screen, the paste is spread over thewhole surface of the screen using a squeegee. In this case, the screenis placed over the printing substrate with a space. Then, the squeegeeis pressed to an extent of contacting the screen with the printingsubstrate and moved to perform printing. Thereafter, the operation isrepeated.

The printed substrate is pre-burned in an oven kept at a temperature offrom 50° to 90° C. In the pre-burning step, the temperature is graduallyraised to a temperature of from 200° to 500° C. at a temperature raisingspeed of from 2° to 20° C./minute and the substrate is maintained at thetemperature for maximum 60 minutes, during which, the decompositionaction of the organic components is controlled. Thereafter, thepre-burned substrate is placed in a belt furnace and burned in anitrogen atmosphere at a temperature of from 750° to 950° C. for 5 to 20minutes (peak keeping time) to sinter the copper powders and adhere thecopper powders to the substrate by causing a reaction.

In addition, in the present invention, by adding a binder resin to theconductor paste, the printability can be improved. As the binder resin,there are, for example, celluloses such as nitrocellulose, ethylcellulose, cellulose acetate, butyl cellulose, etc.; polyethers such aspolyoxyethylene, etc.; polyvinyls such as polybutadiene, polyisoprene,etc.; polyacrylates such as polybutyl acrylate, polymethyl acrylate,etc.; and polyamides such as nylon 6, nylon 6.6, nylon 11, etc.

In the conductor paste of the present invention, the super-fineparticles of copper oxide having particle sizes of not larger than 100nm do not cause separation and precipitation in the paste by theinteraction with the polymer and can adhere to a ceramic substrate bycausing a reaction owing to the high reactivity of the super fineparticles to form a conductor film with a large adhesive force. Also, byadding the mixed copper powders each having a mean particle size range,the auxiliary copper powders contained in the mixed copper powders fillthe voids and spaces formed by the arrangement of the base copperpowders and a conductor film having no inside defects and a good burnedtightness can be obtained.

Furthermore, in the conductor paste added with a glass powder, theadhesive force between the conductor film and the substrate can be moreimproved and also since the addition amount of the glass powder is verysmall as compared with conventional conductor pastes, the conductorpaste of this invention is excellent in the soldering property, theelectric resistance of the conductor film is low, and also since a clearlayer of the glass powder is not formed at the interface between theconductor film and the substrate, the thermal shock resistance is alsoimproved. Also, since the glass powder being used in this invention doesnot contain lead or if the glass powder contains lead, the amountthereof is slight, a soldering treatment for carrying out the oxidationprevention and Au wire bonding can be stably applied.

Also, since in this invention, the conductor paste is coated on thesurface of the substrate and after pre-burning it under temperatureraising, the substrate thus coated with the conductor paste is burned toform a conductor film on the surface of the substrate, pre-burningdecomposes and controls the organic components such as the polymer, theorganic solvent, etc., whereby a conductor film having no insidedefects, a good burned rightness, and a high adhesive force can beobtained. Also, the control of the oxygen concentration at burning isunnecessary.

Then, the present invention is explained in more detail by the followingpractical examples.

EXAMPLES 1 TO 4 (Preparation of High Polymer Composite)

Using a vacuum vapor-deposition apparatus, 5 g of the polymer pellets ofnylon 11 were placed in a tungsten boat and the apparatus was evacuatedto 1×10⁻⁶ Torr. Then, the tungsten boat was heated by applying a voltagethereto to melt the polymer pellets and thus a vapor-deposited highpolymer layer having a thickness of about 5 μm was formed on thesubstrate (glass plate) placed on the upper portion of the bottom standat a vacuum of from 1×10⁻⁴ to 1×10⁻⁶ Torr at a speed of about 1μm/minute. The molecular weight of the polymer layer was from about 1/2to 1/10 of that of the foregoing polymer pellets.

Furthermore, copper chips were placed in a tungsten boat and melted byheating to carry out the vapor deposition at a vacuum of from 1×10⁻⁴ to1×10⁻⁶ Torr, whereby a copper vapor-deposited film was attached onto thepolymer layer. The vapor-deposited substrate was taken out from thevacuum vapor-deposition apparatus and allowed to stand in a chamber keptat 120° C. for 10 minutes to provide a composite. As the result, thehigh polymer composite thus obtained contained 55% by weight Cu₂ O andthe particle sizes of the copper oxide particles in the polymer werefrom 1 to 15 nm.

(Preparation of Conductor Paste)

The high polymer composite containing 60% by weight obtained in theabove step was mixed with mixed copper powders while controlling suchthat the weight ratio of Cu₂ O in the polymer composite to the mixedcopper powders became 1 to 12.5 and the total addition amount of Cu₂ Oand the mixed copper powders became 82% by weight of the conductorpaste. In this case, as the mixed copper powders, four kinds of mixedcopper powders composed of a base copper powder and two kinds ofauxiliary copper powders were used.

After dispersing each of the four kinds of the mixed copper powders inmeta-cresol as an organic solvent with stirring, the dispersion wasfurther uniformly mixed with an ink roll to provide each brown conductorpaste. The content of meta-cresol in each conductor paste obtained was13% by weight of the conductor paste. The compositions of the conductorpastes obtained above are shown in Table 1 below.

(Preparation of Conductor Film)

Each conductor paste obtained above was screen-printed onto an aluminumsubstrate using a screen of stainless steel 300. The substrate thusprinted was pre-burned in an oven kept at 260° C. for 15 minutes.Thereafter, the pre-burned substrate was placed in a belt furnace andburned in a nitrogen atmosphere, at an oxygen concentration of from 0 to10 ppm, a burning temperature of 850° C. for a peak retention time of 15minute to form a conductor film on the substrate.

(Evaluation Method)

The adhesive force of the conductor film and the electric resistance ofthe conductor film after burning, and the thermal shock resistancethereof were measured by the following methods.

1. Adhesive force of conductor film after burning (L-type pealstrength):

A tin-plated copper wire having a diameter of 0.6 mm was fixed on theconductive film formed on the surface of the substrate by soldering in asize of 2 mm×2 mm and the adhesive force of the copper wire bentperpendicularly was measured by a spring balance to determine theadhesive force between the substrate and the conductor film.

2. Electric resistance of conductor film:

A film having a thickness of 15 μm and a diameter of 1.5 cm was preparedand the electric resistance was measured by a four probe method.

The results obtained by the above evaluation methods are shown in Table2 below.

COMPARATIVE EXAMPLE 1

The high polymer composite containing 60% by weight Cu₂ O describedabove was mixed with a copper powder having a mean particle size of 3 μmwhile controlling such that the weight ratio of Cu₂ O in the polymercomposite to the copper powder became 1 to 12.5 and the total additionamount of Cu₂ O and the copper powder became 82% by weight of theconductor paste.

After dispersing the mixture in meta-cresol as an organic solvent withstirring, the dispersion was further uniformly mixed with an ink roll toprovide a brown conductor paste. The content of meta-cresol in theconductor paste obtained was 13% by weight.

Also, a conductor film wad formed on a substrate as in Example 1 and theadhesive force of the conductor film and the electric resistance of theconductor film were measured.

The results obtained are shown in Table 2 below.

                  TABLE 1                                                         ______________________________________                                              Polymer                        Organic                                        Composite  Mixed Copper Powder Solvent                                               Nylon   (weight ratio)    meta-                                        Cu.sub.2 O                                                                           11      7 μm                                                                            5 μm                                                                            3 μm                                                                            1 μm                                                                            0.5 μm                                                                           creso 1                        ______________________________________                                        Ex.1  0.60   0.40    6.485                                                                              --   --   0.260                                                                              0.130 1.20                                                (100)          (4)  (2)                                  Ex.2  0.60   0.40    --   6.486                                                                              --   0.260                                                                              0.130 1.20                                                     (100)     (4)  (2)                                  Ex.3  0.60   0.40    --   --   6.486                                                                              0.260                                                                              0.130 1.20                                                          (100)                                                                              (4)  (2)                                  Ex.4  0.60   0.40    --   --   6.486                                                                              1.30 0.260 1.20                                                          (100)                                                                              (2)  (4)                                  Comp. 0.60   0.40    --   --   6.875                                                                              --   --    1.20                           Ex. 1                                                                         ______________________________________                                         (*): The numeral in the parenthesis in the mixed copper powders shows a       weight ratio.                                                                 Ex.: Example Comp. Ex.: Comparative Example                              

                  TABLE 2                                                         ______________________________________                                                              L-Type Peal                                                                              Sheet                                                              Strength   Resistance                                             Printability                                                                              (kg/2 × 2 mm.sup.2)                                                                (mΩ/□)                      ______________________________________                                        Example 1 good        0.5        1                                            Example 2 good        1.5        1                                            Example 3 good        1.6        1                                            Example 4 good        2.1        1                                            Comparative                                                                             good        1.5        2                                            Example 1                                                                     ______________________________________                                    

As the results thereof, it can be seen that by using the mixed copperpowders, the adhesive force of the conductor film is increased and theelectric resistance thereof is lowered.

EXAMPLES 5 TO 10 (Preparation of Conductor Paste)

The high polymer composite containing 60% by weight Cu₂ O as used inExample 1 was mixed with mixed copper powders while controlling suchthat the weight ratio of Cu₂ O in the polymer composite to the mixedcopper powders became 1 to 12.5 and the total addition amount of Cu₂ Oand the mixed copper powders became 82% by weight of the conductorpaste. As the mixed copper powders, mixed copper powders obtained bymixing a base copper powder having a mean particle size of 3 μm, anauxiliary copper powder having a mean particle size of 1 μm, and anauxiliary copper powder having a mean particle size of 0.5 μm at ablending ratio of 100:2:4 were used.

Also, as a glass powder, various glass frits shown in Table 3 were used.After dispersing the foregoing mixture and the glass powder inmeta-cresol as an organic solvent with stirring, the dispersion wasfurther uniformly mixed with a ink roll to provide each brown conductorpaste. The content of meta-cresol in the conductor paste was 13% byweight.

(Preparation of Conductor Film)

Each conductor paste was screen printed on an alumina substrate using astainless steel screen of 150 mesh. The printed substrate was pre-burnedin an oven. In the pre-burning step, the temperature was graduallyraised from 80° C. at a temperature raising speed of 5° C./minute andthe substrate was kept at 260° C. for 6 minutes, during which thedecomposition behavior of the organic components was controlled.Thereafter, the pre-burned substrate was placed in a belt furnace andburned in a nitrogen atmosphere at a burning temperature of 850° C. for15 minutes to form a conductor film on the substrate.

The adhesive force of the conductor film obtained and the electricresistance of the conductor film are shown in Table 4.

                  TABLE 3                                                         ______________________________________                                        Sample No.  N-1    N-2     N-3  N-4   L-1  L-2                                ______________________________________                                        Particle Size (μ)                                                                      4.6    4.1     5.2  2.3   2.7  2.7                                Softening Point                                                                           585    529     600  673   555  537                                (°C.)                                                                  Thermal Expansion                                                                          67     86      76   49    72   82                                Coefficient (α)                                                         Lead        none   none    none none  used used                               ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                              L-Type Peal                                                                              Sheet                                                  Glass Frit  Strength   Resistance                                             Sample No.  (kg/2 × 2 mm.sup.2)                                                                (mΩ/□)                      ______________________________________                                        Example 5 N-1         5.3        1                                            Example 6 N-2         4.4        1                                            Example 7 N-3         6.3        1                                            Example 8 N-4         3.5        1                                            Example 9 L-1         1.9        1                                            Example 10                                                                              L-2         2.9        1                                            ______________________________________                                    

As the results shown above, it can be seen that in the conductor pastesof this invention, every kinds of the glass frits can be used but byusing the glass frit having a thermal expansion coefficient near thethermal expansion coefficient (α), 76×10⁻⁷ K⁻¹ of the alumina substrate,the thermal shock resistance is excellent.

EXAMPLES 11 TO 15

The high polymer composite containing 60% by weight Cu₂ O as in Example1 was mixed with mixed copper powders while controlling such that theweight ratio of Cu₂ O in the polymer composite to the mixed copperpowders became 1 to 12.5 and the total addition amount of Cu₂ O and themixed copper powders became 82% by weight of the conductor paste. As themixed copper powders, mixed copper powders obtained by mixing a basecopper powder having a mean particle size of 3 μm, an auxiliary copperpowder having a mean particle size of 1 μm, and an auxiliary copperpowder having a mean particle size of 0.5 μm at a blending ratio of100:2:4, and mixed copper powders obtained by mixing a base copperpowder having a mean particle size of 5 μm, an auxiliary copper powderhaving a mean particle size of 1 μm, and an auxiliary copper powderhaving a mean particle size of 0.5 μm at a blending ratio of 100:2:4were used, respectively.

Also, as a glass powder, a glass frit (particle size 5.2 μm, softeningpoint 600° C., thermal expansion coefficient (α) 76, lead free) wasadded to each of the foregoing mixed copper powders in an amount of 0.2%by weight, 0.5% by weight, and 1.0% by weight, respectively, of thetotal amount of copper oxide and the mixed copper powders.

After dispersing each of the mixtures in meta-creosol as an organicsolvent, each dispersion was further uniformly mixed with an ink roll toprovide each brown conductor paste. The content of meta-cresol in theconductor paste obtained was 13% by weight.

The compositions of the foregoing conductor pastes are shown in Table 5below.

(Preparation of Conductor Film)

Each conductor paste was screen printed on an alumina substrate using astainless steel screen of 150 mesh. The printed substrate was pre-burnedin an oven. In the pre-burning step, the temperature was graduallyraised from 80° C. at a temperature raising speed of 5° C./minute andthe substrate was kept at 260° C. for 6 minutes, during which thedecomposition behavior of the organic components was controlled.Thereafter, the pre-burned substrate was placed in a belt furnace andburned in a nitrogen atmosphere at a burning temperature of 850° C. for15 minutes to form a conductor film on the substrate.

The results of measuring the adhesive force of the conductor filmobtained, the electric resistance of the conductor film, and the thermalshock resistance thereof were measured are shown in Table 6 below.

(Evaluation Method)

The thermal shock resistance of each conductor film after burning wasmeasured by the following method.

Ni--Au plating was applied onto the conductor film of each substrate,after solder lapping it, the substrate thus treated was allowed to standin an atmosphere of 150° C. for 30 minutes, and then allowed to stand inan atmosphere of -55° C. for 30 minutes, and after applying the heatingand cooling operations at 1000 cycles. the adhesive force between thesubstrate and the conductor film was determined by the foregoing L-typepeal strength.

COMPARATIVE EXAMPLE 2

As shown in Table 5 below, a high polymer composite was not used, mixedcopper powders obtained by mixing a base copper powder having a meanparticle size of 3 μm, an auxiliary copper powder having a mean particlesize of 1 μm, and an auxiliary copper powder having a mean particle sizeof 0.5 μm at blending ratio of 100:2:4 were used in an amount of 81% byweight of the conductor paste, a glass frit (particle size 5.2 μm,softening point 600° C., thermal expansion coefficient (α) 76×10⁻⁷ K⁻¹,lead free) was used in an amount of 0.2% by weight, 0.5 by weight, and1.0% by weight, respectively, of the mixed copper powders, and nylon 11was used in an amount of 5% by weight of the conductor paste.

After dispersing each of the mixtures in meta-cresol as an organicsolvent, the dispersion was further uniformly mixed with an ink roll toprovide each brown conductor paste. The content of meta-cresol in theconductor paste obtained was 14% by weight.

A conductor film was formed on a substrate as in the foregoing examplesand the adhesive force of the conductor film and the electric resistanceof the conductor film was measured.

The results are shown in Table 6 below.

    ______________________________________                                        TABLE 5 (1)                                                                            Polymer      Mixed Copper Powders*1                                           Composite    (weight ratio)                                                   Cu.sub.2 O                                                                           Nylon 11  5 μm                                                                            3 μm                                                                              1 μm                                                                            0.5 μm                          ______________________________________                                        Example 11                                                                             0.60   0.40      --   6.486  0.130                                                                              0.260                                                             (100)  (2)  (4)                                Example 12                                                                             0.60   0.40      --   6.486  0.130                                                                              0.260                                                             (100)  (2)  (4)                                Example 13                                                                             0.60   0.40      --   6.486  0.130                                                                              0.260                                                             (100)  (2)  (4)                                Example 14                                                                             0.60   0.40      --   6.486  0.130                                                                              0.260                                                             (100)  (2)  (4)                                Example 15                                                                             0.60   0.40      6.486       0.130                                                                              0.260                                                        (100)       (2)  (4)                                Comparative                                                                            --     0.50      --   6.486  0.130                                                                              0.260                              Example 2                      (100)  (2)  (4)                                ______________________________________                                        TABLE 5 (2)                                                                              Organic Solvent Glass Frit*2                                       (weight ratio)                                                                           Meta-cresol     N-3    N-4                                         ______________________________________                                        Example 11 1.20            0.74   --                                          Example 12 1.20            --     0.74                                        Example 13 1.20            0.37   --                                          Example 14 1.20            0.15   --                                          Example 15 1.20            0.74   --                                          Comparative                                                                              1.20                   0.74                                        Example 2                                                                     ______________________________________                                         *1: The numeral in the parenthesis in the mixed copper powders shows a        weight ratio.                                                                 *2: The addition amount of the glass frit is the amount to 100 parts by       weight of the total addition amounts of copper oxide and the mixed copper     powders and shown as parts by weight.                                    

                  TABLE 6                                                         ______________________________________                                              L-Type   Sheet   Thermal Stock Resistance                                     Peal     Resis-  Adhesive Force (kg/2 × 2 mm.sup.2)                     Strength tance   Cycle Number                                                 kgf/2 × 2                                                                        (mΩ/□                                                                0    50   100  200  500  1000                          ______________________________________                                        Ex. 11                                                                              4.6      1       3.7  3.1  3.5  4.1  4.5  2.1                           Ex. 12                                                                              3.5      1       1.5  1.6  1.4  1.0  0.5  0.4                           Ex. 13                                                                              3.9      1                                                              Ex. 14                                                                              1.9      1                                                              Ex. 15                                                                              3.6      1                                                              Comp. 0.1      3                                                              Ex. 12                                                                        ______________________________________                                    

As the results shown above, it can be seen that in the conductor pastesof this invention, even when the content of the glass frit is less than1.0% by weight, the conductor film sufficiently adhere to the substrateafter burning, the electric resistance of the conductor film is low, andthe conductor film is excellent in the thermal shock resistance.

Also, it can be seen that in the conductor paste without using a highpolymer composite, the adhesive force of the conductor film is low.

As described above in detail, in the conductor paste of the presentinvention, the super-fine particles of copper oxide having particlesizes of not larger than 100 nm do not cause separation andprecipitation in the paste by the interaction with the polymer and alsothe conductor paste adheres to a ceramic substrate by causing a reactionowing to the high reactivity of the super-fine particles to be able toform a conductor film having a large adhesive force. Also, by addingmixed copper powders each having a different mean particle size range,the auxiliary copper powders fill the voids and spaces formed by thearrangement of the base copper powders, whereby a conductor film havingno inside defects and having a good burned tightness can be obtained.

Furthermore, by adding a glass powder to the conductor paste, theadhesive force between the conductive film formed and the substrate canbe more improved and further since the addition amount of the glasspowder is very small as compared with conventional cases, the electricresistance of the conductor film is lowered and since a clear layer ofthe glass powder is not formed at the interface between the conductorfilm and the substrate, the thermal shock resistance is improved. Also,since the glass powder contains no lead or if contains, the amount oflead is very slight, the conductive film is excellent in the solderingproperty and a plating treatment, which is carried out for the oxidationprevention and wire bonding, can be stably applied.

Moreover, in the production method of the conductor film of thisinvention, since the conductor paste is coated on a substrate and afterpre-burning the substrate under temperature raising, the pre-burnedsubstrate is burned to form a conductor film on the surface of thesubstrate, pre-burning decomposes and controls the organic components ofthe polymer and the organic solvent, whereby a conductor film having noinside defects, a good burned tightness, and a high adhesive force canbe obtained.

What is claimed is:
 1. A copper conductor paste comprising:a polymercomposite including a polymer and super-fine-granulated copper oxide,said super-fine-granulated copper oxide being dispersed in said polymer;mixed copper powder including base copper powder having a mean particlesize in a range of 1 to 10 μm and at least one kind of auxiliary copperpowder having a mean particle size range smaller than that of said basecopper powder; and an organic solvent.
 2. A copper conductor pasteaccording to claim 1, further comprising glass powder wherein the amountof said glass powder is in a range of 0.1 to 5.0 parts by weight to 100parts by weight of the total addition amounts of said copper oxide andsaid mixed copper powder.
 3. A copper conductor paste according to claim2, wherein said glass powder has a mean grain size in a range of 1 to 10μm and a softening point in a range of 200° to 700° C.
 4. A copperconductor paste according to claim 1, wherein said polymer composite isobtained by preparing a thermodynamically non-equilibrated high-polymerlayer, and after adhering a metal layer of copper onto a surface of saidhigh-polymer layer, heating said high-polymer layer to stabilize thehigh-polymer, whereby super-fine particles of copper oxide, super-finegranulated from the metal layer, are dispersed in said polymer.
 5. Acopper conductor paste according to claim 4, wherein saidsuper-fine-granulated copper oxide is super-fine particles of Cu₂ Ohaving a mean particle size equal to or less than 100 nm, and iscontained in said polymer composite in an amount in a range of 0.01 to90% by weight.
 6. A copper conductor paste according to claim 2, whereinsaid polymer composite is obtained by preparing a thermodynamicallynon-equilibrated high-polymer layer, and after adhering a metal layer ofcopper onto a surface of said high-polymer layer, heating saidhigh-polymer layer to stabilize the high-polymer, whereby super-fineparticles of copper oxide, super-fine granulated from the metal layer,are dispersed in said polymer.
 7. A copper conductor paste according toclaim 6, wherein said super-fine-granulated copper oxide is super-fineparticles of Cu₂ O having a mean particle size equal to or less than 100nm, and is contained in said polymer composite in an amount in a rangeof 10 to 90% by weight.
 8. A copper conductor paste according to claim1, wherein said mixed copper powder includes said base copper powderhaving a mean particle size range of from 2 to 10 μm in an amount offrom 80 to 98% by weight of said mixed copper powder, a first auxiliarycopper powder having a mean particle size range of from 0.7 to 2 μm inan amount of from 1 to 10% by weight of said mixed copper powder, and asecond auxiliary copper powder having a mean particle size range of from0.2 to 0.7 μm in an amount of from 1 to 10% by weight of said mixedcopper powder.
 9. A copper conductor paste according to claim 2, whereinsaid mixed copper powder includes said base copper powder having a meanparticle size range of from 2 to 10 μm in an amount of from 80 to 98% byweight of said mixed copper powder, a first auxiliary copper powderhaving a mean particle size range of from 0.7 to 2 μm in an amount offrom 1 to 10% by weight of said mixed copper powder, and a secondauxiliary copper powder having a mean particle size range of from 0.2 to0.7 μm in an amount of from 1 to 10% by weight of said mixed copperpowder.
 10. A copper conductor paste according to claim 3, wherein saidpolymer composite is obtained by preparing a thermodynamicallynon-equilibrated high-polymer layer, and after adhering a metal layer ofcopper onto a surface of said high-polymer layer, heating saidhigh-polymer layer to stabilize the high-polymer, whereby super-fineparticles of copper oxide, super-fine granulated from the metal layer,are dispersed in said polymer.
 11. A copper conductor paste according toclaim 10, wherein said mixed copper powder includes said base copperpowder having a mean particle size range of from 2 to 10 μm in an amountof from 80 to 98% by weight of said mixed copper powder, a firstauxiliary copper powder having a mean particle size range of from 0.7 to2 μm in an amount of from 1 to 10% by weight of said mixed copperpowder, and a second auxiliary copper powder having a mean particle sizerange of from 0.2 to 0.7 μm in an amount of from 1 to 10% by weight ofsaid mixed copper powder.
 12. A copper conductor paste according toclaim 1, wherein a weight ratio of said mixed copper powder to copperoxide in said polymer composite is in a range of 5 to 50 to 1 of copperoxide, and a total addition amount of copper oxide and said mixed copperpowder is in a range of 50 to 90% by weight of said conductor paste.